How much can I expect to pay for a microscope for children? The minimum price for a useable microscope is around EUR 150/USD 200 and up. You would probably like to spend a bit more, but cheaper devices also exist which provide a useful picture, but may be less convenient and stable to use. EUR 300/USD 400 should give you already a very decent device. This is the price that many educational microscopes in schools have. Anything much less than EUR 150/USD 200 is likely not to be of sufficient quality, but simply because a microscope is expensive does not mean that it is automatically suitable. Specialized optics may quickly drive the price up, but may not be suitable or required. If you are buying blindly then you may spend money on unnecessary things, or waste money on a quite useless device. As a matter of fact, some individual microscope objectives can be more expensive than the whole microscope (microscopes are modular).

How are cheaper microscopes different from more expensive ones? Modularity of the microscope, use of more specialized objectives and optics (plan objectives, apochromatic objectives… not needed for children) and quality of machining as well as brand name drive the price up. Devices containing many metal parts are more stable but also more expensive to manufacture.

What can I expect to see under the microscope? This depends to a large extent on three factors: The type of microscope (stereo or compound), the quality (resolution) of the optics and (of course) the specimens that you look at. The type of microscope determines to a certain extent also the specimens that you can look at. With stereo microscopes you can observe opaque objects, such as rocks, whole plant parts or insects. With compound microscopes you can observe the much smaller cells.

Which type of microscope, stereo or compound, should I buy? The choice of the right microscope type (stereo vs compound) is a fundamental issue. After all, you do want to keep the child interested. Buy stereo microscopes if the child is very young (up to 10 years) or if you want to do uncomplicated natural observation without much specimen preparation. Buy stereo microscopes also if you want to extend an already existing hobby or interest such as stamp collecting, collecting coins, minerals, rocks, insects and butterflies or plants. These objects can all be directly viewed under the stereo microscope, without destroying them. Buy compound microscopes if you or your child is also interested in specimen preparation or if you are interested in seeing smaller objects. Older children may be more interested in compound microscopes, as this is the kind that gives more “interactivity” and more possibilities for preparing specimens. Older children may also be interested in making a slide collection. The children can use different magnifications and have to learn to operate both the coarse and fine focus knobs. If you want to to observe water samples and cells, then compound microscopes are the way to go. Be aware that some children may not consider stereo microscopes as “real” microscopes and that they may be disappointed if they are not able to observe paramecia and other small water life that they read about in books. Also be aware that compound microscopes need more guidance and practice, especially if specimens are to be prepared. Many of the following FAQ will deal with compound microscopes. For more information about these two types of microscopes, read: Types of Light Microscopes.

Where can I buy microscopes? Microscopes can be bought from specialized microscope dealers. These often also supply schools and universities with microscopes. Do not buy second hand devices unless you really know what you are doing. There are simply too many things that can go wrong, even if the quality of the second hand microscope is otherwise quite good. It’s well possible that second hand microscopes are equipped with specialized objectives that are not suitable (or simply too expensive) for children. Unlike consumer products, which come out of the box, microscopes are commonly assembled according to the research needs and second hand microscopes may have a research or medical background. It is probably best to personally get advice from a microscope shop.

Is there one single criterion that I should look out for when buying a compound microscope? Look for two things in microscopes. The microscope should be made of metal (and be heavy) and the objectives should be DIN standard. Look at the objective of the microscope and check if it has the number 160 written on it. This refers to a 160 mm tube length. Microscopes that are able to accept these optics often (not always) have a minimum quality. Most educational and routine microscopes use these, plastic toy microscopes do not. These objectives are interchangeable with each other. Microscopes that use infinity corrected objectives have an infinity sign printed on them and are expensive and can be found more on research microscopes. I just mention this for the sake of completion. The material of which the body of the microscope is made is also relevant. Devices made mostly of plastic can be considered toys, and these do not provide the stability and optical quality to keep children interested over a longer time period.

Do my children need support? A microscope is a scientific instrument and it use requires appropriate education and support. After all, inappropriate handling may damage the device (crashing the objective into the slide, for example). Sooner or later the child will have observed all the provided slides and samples and will want to observe new things. Guidance is then needed to prepare more samples (unless you buy ready-made slides). Safety issues must also be considered: How can you protect the microscope and how can you protect the child? Some chemicals used for preparing samples are toxic, do not use them and do not blindly trust them. There are also many non-toxic alternatives around, however, and the parent may need to do a bit of research. There is also the danger of cutting oneself, when preparing samples. You may also need to do some research on the different types of specimens that can be observed – yes a microscope does require some guidance.

Should I buy a second hand microscope? Unless you have worked with microscopes yourself and unless you know what you are doing, I would not buy them second hand. Maybe you know a trustworthy second hand dealer, in this case I would also take second hand microscopes into consideration. Be aware that a quality second hand microscope (such as the “Zeiss Standard”) can be obtained for a fairly low price, but that this microscope provides much greater value than new no-name devices, which may be more expensive. Without advice you run the risk of buying a microscope with objectives that are not appropriate for education, or microscopes that are not operating reliably. There is no way to see from a picture if the objectives are intact, if there is no stage drift and if the gear operate smoothly. Hospitals and research institutions sometimes sell useful used microscopes, but these may be equipped with specialized optics. Also do not buy microscopes from people who do not know much about them. Non experts are not able to assess the quality of a microscope. There are so many things that you have to look out for, that it is not possible for me to summarize this in a few lines. I may write a second FAQ about them.

Is there anything that I should not buy? Do not buy second hand microscopes unless you also buy them from a shop, which is able to give warranty and service. Do not buy specialized microscopes such as inverted microscopes, metallurgical or polarizing microscopes. Again, if you search Ebay, you may not always know the difference. Do not buy scopes that have only a mirror instead of a lamp. Kids may point them to the sun and destroy their eye sight. Mirrors also do not provide enough light intensity. Do not buy historical microscopes. They should go into the museum and also may not have the optical quality (fungal growth on the optical surfaces is a problem, etc.).

What’s the problem with plastic (“toy”) microscopes? These are microscopes that are sold in a colorful cardboard and Styrofoam box together with a wide range of different accessories. There is a general agreement among enthusiast microscopists and teachers that these microscopes should not be bought. First, they are not as cheap as one may think and for a little more money one can already obtain a microscope with substantially better optics. Toy microscopes are often difficult to focus often lacking a coarse and fine-focus knob. Do not forget, that the tolerances of the mechanics has to be extremely narrow. Plastic gears simply can’t keep up with metal gears. They do not have standardized objectives and the resolution of the picture is low. Often the magnification is also advertised as unrealistically high (1000x). The low light intensity (battery operated or mirror) makes it difficult to see the specimens properly. If money is indeed an issue, then it’s better to get a simple but solid stereo microscope. They are more fun to use. In my opinion, children need stable and solid devices that produce a sharp, contrasty and bright image. Kids are demanding these days. The images that the microscope produces has to compete with the strong visual impressions from television, the Internet and magazines. A low-contrast, washed-out, dark picture produced by a toy microscope will not captivate the children for an extended time. My 2 cents. Download Microbehunter Magazine (November 2011) for a comparison between toy microscopes and more suitable microscopes.

I already bought a toy microscope! What should I do? Keep it and buy a “real” one and compare the image quality. Then write an article about it for this magazine.

Where can I save money? You do not need: Köhler illumination (for photography through the microscope), 100x oil immersion objective (more expensive and difficult to use for children). Actually I really dis-advise getting a 100x oil immersion objective. This requires the use of immersion oil, which is messy to use and has more specific applications. You also do not need phase contrast and DIC, these are expensive anyway. Plan objectives are more expensive and useful for photography. I mention this, because second-hand devices may come with these. A bright-field condenser with a filter holder beneath the stage is highly recommended, however. This allows for simple dark-field microscopy (bright specimen on dark background), if you insert a dark-field patch-stop into the filter holder. A device with a mechanical stage (and not only stage clips) is very recommended. It makes operating the microscope easier. A mechanical stage allows you to move the specimen slide horizontally and vertically by turning two knobs.

Which objectives and eyepieces should I buy? Buy achromatic DIN objectives with the magnifications 4x, 10x, 40x and a 10x eyepiece. A 100x oil immersion is not needed and may even be counter-productive. This objective requires advanced techniques and is more expensive. Better to get a 60x objective instead (more rare), but this is optional. This is a standard combination and microscope dealers supplying for schools will already offer these combinations.

Should I buy a microscope with a “name” or a no-name device? This is a long question to answer and the opinions diverge on this issue. From a quality perspective, all “big four” microscope manufacturers (Olympus, Nikon, Leica, Zeiss) produce quality microscopes and also have cheaper introductory microscopes for schools in their program. Still the cost of these microscopes is often higher, but also their resale value. Many no-name devices do carry the name of the importer, and the quality can cover a wide range. I personally have a rather pragmatic view on the issue. If one wants is not able or willing to spend much money on a microscope, then a “no-name” device is probably the only way to go (unless one buys second hand). Some people think that it is better to buy a used “big four” microscope than a new “no-name” microscope of the same price, also because of the higher resale value. I would dare to say that for beginners it may be very difficult to judge the quality of a used device. Of course one can also buy used (and well serviced) microscopes from a dealer, and this is indeed a possibility.

During my beginning days of microscopy, I once talked to a “big four” microscope manufacturer. I was quite surprised that he gave me a surprisingly balanced advice on which microscope combination to buy. He could easily have sold me a microscope which would have been much more expensive (and also not suitable for my needs). I was a beginner. The salesman was quite honest and told me that they have no interest in selling me a microscope which is too expensive and not suitable, for the sake of earning quick money. I summarize his words: “We have a long-term view. The beginning microscopy users of today are the researchers of tomorrow. We want to keep beginners and children interested in microscopy. If the microscopy enthusiasts have a good view about our company (and do not feel ripped-off), then they will also purchase our microscopes when they are in a position to decide if they should equip a whole laboratory with microscopes.” Interesting point.

What about “computer microscopes” Back in 1999, Intel introduced the QX3 Play microscope, which needed to be connected to a computer. The QX3 was later replaced by the QX5. You can read an extensive QX5 USB microscope review here. The image quality of this device seems to be good, and I already have read several positive reviews about this device. It has the advantage that this microscope is able to cover both worlds, the world of compound and of stereo microscopes. Still, these microscopes are sold as “toys” and (according to a review I read) are not able to provide the same image quality as dedicated student and educational microscopes (of comparable price). A disadvantage is, that it is necessary to connect the device to a computer in order to see something (it has no eyepiece). Microscopes like these are not standard and if you want to teach children proper microscopy use (operating the fine and coarse focus, operating the diaphragm, changing objectives, proper microscope cleaning, etc.) then I would get a standard device. You can also take pictures through a regular microscope with a compact camera using afocal photography.

What accessories are needed You also need: an introductory book about microscopy (to keep the children motivated), slides and cover glasses, and tweezers. These things are not expensive. I also highly recommend that you get a slide box with ready-made samples from a wide range. Do not get slides made for medical students, which show a wide range of different anatomical sections (boring). Get slide boxes that contain both plants, insects, animal tissue, water samples, sand, radiolaria, etc, etc. To keep the children interested. This way the children have something to look at right away, without the need to prepare slides on the day they receive the microscope.

This all may sound complicated. What is the easiest approach? Find a dedicated shop selling microscopes and contact them. Often educational supplies companies will have several microscopes in their product range. Other companies are specifically specialized for microscopes. Study the catalog, do some research (your kids will need support preparing the samples anyway). Write them an email and be honest about the needs. Tell them that you need a scope for your kids and also tell them if it should be a compound or stereo microscope. A serious dealer will know the requirements and will not sell you an inappropriate device. They are interested in long term customer relationships and not in quick money.

Comments and opinions are appreciated!

A variety of different standards exist:

• Standard slide: 26 x 76 mm
• Geological slide: 75 x 50 mm
• Petrographic slide: 46 x 27 mm
• Thin sections slide: 48 x 28 mm

Microscope glass slides may be modified in a variety of ways:

• They may have a central indentation to carry several drops of liquid.
• They may have a frosted side to allow for easier writing with a marker.
• They may have polished corners to reduce the possibility of injury due to sharp corners.

Cover glasses (cover slips) exist in a wide range of different sizes, square, round, rectangular. Common sizes include:

• 18x18mm
• 20x20mm
• 22x22mm
• 24x24mm
• various rectangular sizes up to 24x60mm to cover nearly the whole slide.

Choose a cover glass that corresponds to the size of the specimen and the slide. The thickness of the cover glass is important, as it has a significant impact on the resolution of the image. The thickness should correspond to the thickness indicated on the objective lens. In many cases, the cover glass is 0.17mm thick, but there is often a small variation even in the same batch. For critical purposes, it may be necessary to measure the thickness of the individual cover glasses to find one close to the desired thickness (use a vernier caliper to determine the thickness).

There are several very useful accessories that I recommend for each workplace. 1: tweezers; 2: dropper; 3: scalpel; 4: watch glass; 5: slides; 6: blue filter; 7: cover glasses; 8: needle; 9: scissors; 10: small petri dish; 11: plastic tray

I recommend the following accessories for each microscopic work place:

1. Tweezers: They are useful for placing the cover slip on the specimen and for picking up small specimens (insects, thin cuts, etc.).
2. Dropper: For placing a water drop between the slide and cover glass.
3. Scalpel: Useful for cutting away not needed plant tissue or algae. Do not include for young children.
4. Watch glass: For storing water for making temporary slides.
5. Slides: There are several types available. Some have a frosted side to allow for easier writing, others have rounded edges to decrease the possibility for injury.
6. Blue filter: Useful for compensating the red tint of old tungsten lamps.
7. Cover glasses: obtain those that correspond to the objectives. 0.17mm thickness is standard.
8. Needle: Useful for separating algae or to pick up very small samples of material to be observed.
9. Scissors: For cutting filter paper to remove excess water.
10. Small petri dish: For the storage of specimens that need to be kept in water (plant material, algae, pond water etc.). Cuts of plant material are stored in the dish before they are observed.
11. Plastic tray: For storing the above accessories.

The following accessories are also commonly used, but may not be recommended or necessary for each individual workplace. Safety is an issue as well!

• Razor blades: for making cuts through leaves and stems. Too dangerous to be stored in every workplace, and not always needed.
• Stains: Some stains are toxic, especially those that are used to stain the DNA inside the nucleus of cells (possibly carcinogenic!). Some may stain clothing irreversibly.
• Mounting media: These are used to make permanent mounts. They may contain organic solvents which are not healthy when inhaled. There is also the danger that students confuse them with the immersion oil…..
• Eldermarrow, styrodur or styrofoam: These are used to make thin cuts of plant material. The plant material is squeezed between two layers of this material and then cut. Eldermarrow is recommended. Styrodur and styrofoam also work but they are very tough on the razor blades and will make them dull extremely quickly.

Stained nuclei of plant cells. Check if the optics deliver a crisp picture of high contrast. Is dust visible?

Before buying a second hand microscope, take care of the following points. The list is certainly not complete, but should give an overview of the things to look out for:

• Appropriate optics: Make sure that the microscope is equipped with the objectives that are needed for your task. Many microscopes from hospitals and research institutes are equipped with phase contrast or plan apochomatic objectives. These are expensive and not required for educational work.
• Are the focusing knobs easy to turn or has the lubrication oil already solidified? Do not force-turn the focus knobs, it will increase the wear on the gears.
• Does the condenser move freely up and down, or has the lubrication oil already solidified? Does the condenser stay up, or is it pulled downwards by its own weight?
• Does the iris diaphragm open and close without problems, or has the lubrication oil already solidified?
• Were the non-oil immersion objectives dipped into immersion oil? They are not designed for this.
• If the objectives are spring-loaded, does the front part of the objective retract properly when pushed in? Or was the objective covered completely with immersion oil, now solidified?
• Are there any fungi growing on the lens optics? This may be a problem of microscopes used in warm and humid areas.
• Does the stage stay where it is, or does it move down due to its own weight?
• Does the microscope generally make a good impression?

Additional points to consider for schools:

• If you want to equip a whole classroom with used (or new) microscopes, make sure that they are from the same series. Students are then confronted with the same device each time and do not have to re-learn the peculiarities of each instrument – more productive lab work. It also makes makes it easier for the teacher to explain the handling of the microscope. If you buy used instruments, then you may not be able to obtain a whole classroom set at once (unless another school, college or hospital replaces its equipment at once).
• Make sure that the used microscopes have the appropriate optics installed and not specialized objectives! You need achromatic bright-field objectives. Many research microscopes come with phase contrast objectives installed, however. This type of optics also can be made to work like bright-field objectives but they are more expensive and you don’t want to spend money on things that you don’t need.
• In recent years the so-called infinity optics became increasingly popular, especially in research. Be careful – infinity objectives are not compatible with the “traditional” DIN 160mm systems, and infinity optics from different manufacturers are also not compatible with each other. When purchasing infinity systems (if you can afford them…), be aware that the optics can possibly not be exchanged with other microscopes that you or your school owns.

A polyp. Inverted colors, not darkfield.

Occasionally people ask me for advice about which type of microscope to buy as a present for their children. I once responded to a newsgroup question making a very strong point in favor for stereo microscopes for young children (approx. 5 years of age), and I would like to reiterate these points below. Read the article “Different Types of Light Microscopes” for a description of similarities and differences between the different microscope types. The following section reflects my own personal opinion on this issue.

In any case, I do not recommend the purchase of “toy” microscopes. If you invest a little more you are able to obtain a “real” instrument with substantially better image quality and flexibility, one which will retain the interest of the child (and parent!!) for a longer time. And especially for children a good image quality is necessary. An experienced microscopist may be able to interpret the “dark washed-out blob” as a cell, but children need crisper and clearer images to maintain their fascination – my personal opinion. There is the danger of disappointment if they do not see similar images as those printed on the box, and I am almost certain that many “toy microscopes” are not capable of keeping their promise. But this is my personal opinion, and the quality of these devices certainly varies as well.

Some of these microscopes are also sold with unrealistic magnifications up to over 1000x. Please understand that toy microscopes are useless at this magnification, for a range of reasons:

• Resolution is too low: The object that you want to see is magnified 1000x for sure, but you only see a washed-out blob with no detail.
• Stability is low:. There is a good reason why microscopes are made of metal and why they are heavy. Every vibration (walking) is magnified as well and transferred to the microscope.
• Image is dark: A high magnification requires a high light intensity. Many of these microscopes are not capable of delivering the required light intensity.
• And: bad depth of field, optics not corrected for lens errors, etc. etc.

I have to admit that even “toy” microscopes vary greatly in quality (and price). If you want to buy one of these, then I would recommend you not to give magnifications above 200x or 400x much weight and to read appropriate reviews beforehand. A cheap plastic scope with 1000x magnification is unrealistic. I have already seen some better quality “toy” microscopes but the price difference to a microscope manufactured according to the international DIN standard was not too big. The bottom line is that the child should enjoy working with the instrument.

Compound or Stereo Microscope?

Instead of simply listing the pros and cons of each type, I’ll make life easy by giving you two simple rules:

The younger the child the more you should tend towards stereo microscopes.

and:

If you intend to purchase a compound microscope, make sure that it works with the DIN standard. This allows for an exchange of objectives and guarantees a minimum quality.

There are many points that speak for stereo microscopes for young children, they are not only more “child friendly”, and more forgiving and easier to handle:

• The subjective visual impression of 3D samples (flies, hair, rocks etc.) can be quite fascinating. The view is, in contrast to compound microscopes, upright (!). A big advantage for orientation.
• Little to no sample preparation required for many objects. There is no need to cut and slice the specimens into the required thickness, even though this is possible as well. There is no need to prepare specimen slides with cover-slips. We use stereo microscopes in our school, and as a first introduction, we gave our students a post card and made them look at the colored dots that compose the image – fast, simple with an immediate result.
• Stereo microscopes have a low magnification, often not more than 40x. This means that there is less abstraction “from the real world”. A fly looks like a fly, only much bigger and more impressive. For a compound microscope you need to take the fly apart first and examine the individual parts, it’s too thick otherwise to be observed.
• Stereo microscopes also allow for an observation of non-transparent objects like rocks, fingernails (the dirt is pretty interesting…), skin, plant leaves etc. Stick a whole earth worm under the microscope and see how it looks like. Directly observe a dish of pond-water. If the child is already collecting rocks, insects, stamps, coins, etc. then a stereo microscope is the natural extension to observe these collected items.
• Some stereo microscopes also allow for a change in magnification, by zooming. This is not a necessity, though.
• Decent stereo microscopes can be cheaper than compound microscopes, because they are less complex.
• Stereo microscopes need less time for instruction. More instruction time needed for compound microscope. With compound microscopes, if you use a higher magnification and then turn the coarse-focus-adjustment knob into the wrong direction, you run the risk of ruining both sample and objective because you smash the objective into the specimen. Stereo microscopes have a large sample-objective distance.
• Stereo microscopes have a higher depth of field. It is therefore much easier to find what you are looking for.

Stereo microscopes also possess certain disadvantages:

• There may be some samples that you or your child is interested in but requires a higher magnification. For example, if you want to watch the nucleus of cells, then you are better off with a compound microscope. It is also not possible to observe bacteria, they are simply too small. As a comfort, a compound microscope with regular bright-field optics also does not allow you to view living bacteria, as they are transparent, you need expensive phase-contrast objectives (labs use them). Alternatively the bacteria have to be stained first, and then I doubt that novices will be able to recognize them as bacteria.
• Sample preparation may indeed be one of the activities that a child may be interested in, but stereo-microscopes do not require much preparation, while it is necessary in compound microscopes.
• Some younger children may have problems viewing through both eye-pieces (they can look through one of them if they want to).
• And possibly the biggest “problem”: There is the myth that microscopes have to magnify very much in order for the person to see much. Children may be disappointed if they hear that their stereo microscope only magnifies up to 40x, if their friend has a department store (“toy”) microscope which magnifies 1250x. This is where education comes into play – magnification is not everything, and a high magnification does not mean that one sees more, resolution also counts. I want to guarantee you that you won’t be able to see much at 1250x.

Buttercup Plant

The equipment of a lab with microscopes can be a costly affair. In order to avoid misinvestment, several important decisions that must be taken into consideration:

• The type of microscope: compound or stereo microscope
• The number of microscopes
• Curriculum
• The manufacturer of the body and optics
• The features of the microscope

The type of microscope: The decision between compound and stereo (dissecting) microscope is a central issue. I would make this decision based on the age or grade level of the students. I do not recommend the use of compound microscopes for very young students, for a variety of reasons. If primarily elementary school to lower middle school students are to use the equipment, it may be well worth considering to purchase stereo microscopes only. Compound microscopes demand more extensive sample preparation (unless purchased slides are used) and more experience in handling and are thus more suitable for older students. There are also paedagogical issues related to the choice of the type of microscope. Stereo microscopes supply a three-dimensional upright image at a lower magnification. Parts of the specimens that can also be seen using the naked eye can now be observed much larger. It is much easier for the students to imagine size relationships this way. Schools with sufficient budget purchase both types of microscopes.

The number of microscopes: How many devices should be purchased? This is not only a budget issue. The costs of microscopes can vary greatly and it is easily possible to obtain 20 cheap devices for the same amount of money as 5 expensive instruments. What is the class size? How many students should use one microscope? How much storage space is available? What are the curricular demands? This question can not be easily answered an a few lines. I would recommend one microscope per 2 students. For a large class of approximately 30 students, this would mean 15 instruments. If the school intends to purchase both stereo and dissecting microscopes, storage space for 30 instruments must be available.

Curriculum: What skills should the students learn? Are sample preparation, staining, making specimen cuts a part of the curriculum? If yes, then there is probably no way around a compound microscope. Should rocks, insects and every-day objects be observed? In this case it may be more suitable to obtain stereo microscopes.

The manufacturer of the body and optics: There are many manufacturers that supply schools with comparatively cheap devices. Often the optics are not manufactured by these companies but purchased from specialized firms and included in the set. In my view the brand of the device is of minor importance. Available servicing is a much more important factor to consider. While microscopes generally do not require much maintenance, it may be necessary to readjust some of the parts periodically. Over the years the oil becomes thick and the focussing knobs become difficult to turn. A firm that is willing to perform the routine maintenance makes life for the teacher easier (unless the teacher him/herself is capable of maintaining the equipement).

Sunflower stem

When purchasing instruments, look out for the following:

• Stability: Make sure that the construction of the decive makes a solid impression. A solid device minimizes vibrations. Do not forget that even vibrations are amplified by the magnification.
• Mechanics: The focus knobs and X/Y knobs should turn easily and without friction. Is there any play when turning the knobs? Does the stage stay in place or does it shift? If the stage changes position due to gravity, then a readjustment is necessary. Does the revolving nosepiece center the objecitves properly? Is there any play in the nose-piece?
• Optics: Is the resolution and the contrast of the objecitves sufficient? Also make sure that the objectives are of the same series so that parfocality is guaranteed. Is the field-of-view of the eye piece large enough?
• Lighting system: Does the light intensity correspond to the objecitves? A higher light intensity is required for higher magnifications. A halogen lamp delivers a brighter image. This is an advantage if students are required to work much with the 100x objecitve.
• Student Proofing: A student proofed microscope requires special tools for the removal of eyepieces and other components. There are no finger-screws to turn, everything must be adjusted using the tools.

Notice that I did not include maximum magnification as one criterion. This is the least important aspect. In most circumstances a total maximum magnification of 400x is absolutely sufficient.

If your school decides to purchase used microscopes – hospitals and research institutions occasionally replace their equipment – then take care of the following points as well:

• Are the knobs difficult to turn? This is an indication that the lubrication oil has started to solidify and must be replaced. Do not turn the knobs with force, as this may damage the gearing.
• Check if the mechanics demonstrate excessive play. Over time there is a natural wear of the gearing.
• If dust is visible then the optics must be cleaned with pressurized air.
• Microscopes that were used in a humid environment may start to grow fungi on the optical surfaces. Some optics are sprecially treated with anti-fungal substances to prevent this from happening.